1. Technical Field
The present disclosure relates to method of recording data in an optical data storage medium. More particularly, the present disclosure relates to method of recording microholographic data in a holographic storage medium.
2. Discussion of Related Art
Holographic storage is optical data storage in which the data is represented as holograms, which are images of three dimensional interference patterns created by the intersection of two beams of light in a photosensitive medium. More particularly, the superposition of a reference beam and a signal beam, containing digitally encoded data, forms a 3-D interference pattern within the volume of the medium resulting in a chemical reaction that changes or modulates the refractive index of the photosensitive medium (recording or writing step). This modulation records both the intensity and phase information from the signal as the hologram. The hologram can later be retrieved by exposing the storage medium to the reference beam alone, which interacts with the stored holographic data to generate a reconstructed signal beam proportional to the initial signal beam used to store the holographic image (reading step).
Recent research into holographic data storage has focused on a bit-wise approach for recording data, where each bit (or few bits) of information is represented by a hologram localized to a microscopic volume within a medium to create a region that reflects the readout light. Such localized volume holographic micro-reflectors may be arranged into multiple data layers throughout the volume of the medium. Materials capable of accommodating a bit-wise data storage approach are highly sought after as the equipment utilized to read and write to such material is either currently commercially available, or readily provided with modifications to commercially available reading and writing equipment.
However, conventional methods of storing bit-wise holographic data employ linear photosensitive materials or materials susceptible to photochemical change independent of the power density (intensity) of incident radiation. These linear materials are also susceptible to photochemical change at both the writing and reading conditions. Moreover, in the bit-wise approach, the readout and recording of data in the layers inevitably leads to exposure of the adjacent layers to the recording/readout radiation. Therefore, conventional methods of recording/reading bit-wise holographic medium using linear materials could lead to unintended erasure or data loss in the medium during recording/reading.
Thus, there is a need for methods of recording data in a holographic storage medium data without affecting other layers of data during the writing step. Further, for bit-wise approach of recording holographic data, there is a need to have separate write and read conditions, such that the reading step does not adversely affect the recorded data.